This invention relates to a pneumatic brake for railway locomotives and motor cars which are equipped with an additional brake, preferably electric brake.
Existing systems include a shut-off valve arranged in a brake pressure line between a brake control valve, which is controlled by the pressure in a main air pipe, and at least one brake cylinder. The shut-off valve in a first switching position, which corresponds to an inoperative additional brake, connects the brake control valve to the brake cylinder and in a second switching position, which corresponds to an operative additional brake, disconnects the brake control valve from the brake cylinder and connects the brake cylinder with the atmosphere.
Generally, the additional electric brake is an electric generator brake, but it may also be an eddy current brake or a hydraulic brake. This additional brake generally operates without wear and/or it permits energy recuperation. Because of this favorable behavior, the additional brake is operated when the locomotive or motor car is braked. It is only when the effect of this additional brake is no longer sufficient that the pneumatic brake is actuated in addition or alone. The braking effect of the additional brake may no longer be sufficient, for example, in the case of very high braking requirements, at very slow driving speeds or when the additional brake fails. When braking is required, the brake control valve of the pneumatic brake as well as the additional brake are actuated. When the additional brake is operative, the shut-off valve keeps the brake cylinder line bled and, despite the response of the brake control valve, excludes a braking by the pneumatic brake. The pneumatic brake is therefore kept back. However, there is the danger that, when the control of the shut-off valve is faulty or when it malfunctions, for example, by mechanical jamming, the passage through the brake pressure line cannot be restored when the additional brake is inoperative. Thus, a braking effect can no longer be achieved by the pneumatic brake. The danger therefore exists that the brake of the locomotive or motor car may fail completely.
Thus, it is an object of the invention to develop a pneumatic brake of the above type such that the above-mentioned danger of a failing of the pneumatic brake with respect to its braking effect is avoided when the additional brake is inoperative.
According to the invention, this object is achieved in that a by-pass valve is provided which is parallel to the shut-off valve. The by-pass valve is opened only during an actuating or controlling of the pneumatic brake which exceeds a control range and opens up the passage through the brake pressure line irrespective of the switching condition of the shut-off valve. The connection of the brake cylinder line section of the brake pressure line with the atmosphere by the shut-off valve is at least choked when the by-pass valve is opened up.
The by-pass valve ensured that, when a rapid braking is initiated by the main air pipe which exceeds the control range of the pneumatic brake, even when the shut-off valve malfunctions, a passage to the brake pressure line is always opened up, and the brake control valve can therefore control a brake pressure into the brake cylinder. The throttling or the blocking of the atmosphere connection of the brake cylinder line section ensures that, at least until the locomotive or motor car stops, a sufficiently high pressure admission to the brake cylinder is maintained.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.